Slow watering long range sprinklers are often used to irrigate large areas such as farms, lawns, golf courses and the like. One commonly used irrigation device is an impact sprinkler having a vane, hammer and anvil assembly to provide motive force for rotating a sprinkler head. The vane pivots on a shaft centered on the assembly and is spring-loaded. The spring in the at-rest condition positions the vane into the path of a solid stream of water directed generally upward and outward. The stream forces the vane to rotate in a direction opposite to the desired sprinkler head rotation. The spring limits this vane rotation and returns it to the at-rest position for repetition. As the vane reaches the at-rest position the attached hammer strikes an anvil which is attached to the sprinkler head. The degree of rotation is limited by the inertia of the hammer and sprinkler head and by a compression spring which loads a thrust bearing upon which the sprinkler head rotates. Thus, in this device the sprinkler head is caused to slowly rotate in a series of small steps.
In irrigating large areas it is necessary to evenly distribute the water flow to the area being sprinkled. In the prior art device described above, the vane moves into and out of the stream breaking the stream into small drops. The velocities of the drops thereby produced are much lower compared to the velocity of the stream, and thus the drops fall to the ground after traveling relatively short distances. These drops provide short and intermediate sprinkling of the area being irrigated. The stream irrigates at long range with large drops during intervals when it is not in contact with the vane. Impact sprinklers commonly provide somewhat less water at intermediate ranges than at short and long ranges. Further, moving parts require maintenance and wear out, causing premature failure of the sprinkler.
A need has thus arisen for a large area irrigation sprinkler that is simple in operation, low in cost, and effective in short, intermediate and long range irrigation.